Mumbai University > Electronics Engineering > Sem6 > Computer Organization

Marks: 5M

Year: Dec 2015

The different addressing modes 8085 are as follows:

1) Immediate Addressing Mode:

• In this addressing mode, the 8 bit /16 bit data is specified in the instruction itself.

• Instructions can be 2 byte or 3 byte long. In 2 byte instruction, first byte is OPCODE and second byte is 8 bit data. In 3 byte instruction, first byte is OPCODE, second and third byte is 16 bit data.

  Example:

  MVI A, 05 H

  This instruction transfer immediate data (05H) in Accumulator.

2) Register Addressing Mode:

• In this, the source and destination operands are general purpose registers.

• Register addressing instructions are generally of 1 byte i.e. OPCODE only. OPCODE specifies the operation and registers to be used to perform the operation.

  Example:

  MOV D, B

  This instruction copies the contents of the register B to register D.

3) Direct Addressing Mode:

• In this instruction mode 16 bit address of the operand is given within instruction itself.

• The instruction in the direct addressing mode are 3 byte instructions. First byte is OPCODE, second byte is lower order address and third byte is higher order address.

  Example

  STA 3200H

  Stores the contents of accumulator into memory loacation 3200H.

4) Indirect Addressing Mode:

• In this mode the address of the operand is specified by a register pair.

• Example:

  LXI H, 3200H; Load HL pair with 3200 H

  MOV A, M ; Move the content of memory location pointed by HL register pair into accumulator.

5) Implicit Addressing Mode:

• This addressing mode does not require any operand.
• The instructions of Implicit Addressing mode are 1 byte.

• Data is present in accumulator.

  Example:

  i) complement the accumulator

  ii) Complement carry.